Syzbot has been reporting the problem of stack-out-of-bounds in
profile_pc for a long time:
https://syzkaller.appspot.com/bug?extid=84fe685c02cd112a2ac3
profile_pc tries to get pc if current regs is inside lock function. For
!CONFIG_FRAME_POINTER it used a hack way to get the pc from stack, which
is not work with ORC. It makes profile_pc returns wrong result, and
frequently triggers KASAN.
This can be fixed by using the unwind_start, it will skip the first
regs frame and get the caller of lock function directly, or 0 if
unwind_get_return_address finds the unwinding failed. For all of FP, ORC
and guess unwinders it works.
Fixes: 0cb91a229364 ("[PATCH] i386: Account spinlocks to the caller during profiling for !FP kernels")
Reported-by: [email protected]
Signed-off-by: Chen Zhongjin <[email protected]>
---
arch/x86/kernel/time.c | 20 ++++++--------------
1 file changed, 6 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
index e42faa792c07..5e0446f49906 100644
--- a/arch/x86/kernel/time.c
+++ b/arch/x86/kernel/time.c
@@ -24,26 +24,18 @@
#include <asm/timer.h>
#include <asm/hpet.h>
#include <asm/time.h>
+#include <asm/unwind.h>
unsigned long profile_pc(struct pt_regs *regs)
{
unsigned long pc = instruction_pointer(regs);
if (!user_mode(regs) && in_lock_functions(pc)) {
-#ifdef CONFIG_FRAME_POINTER
- return *(unsigned long *)(regs->bp + sizeof(long));
-#else
- unsigned long *sp = (unsigned long *)regs->sp;
- /*
- * Return address is either directly at stack pointer
- * or above a saved flags. Eflags has bits 22-31 zero,
- * kernel addresses don't.
- */
- if (sp[0] >> 22)
- return sp[0];
- if (sp[1] >> 22)
- return sp[1];
-#endif
+ struct unwind_state state;
+
+ /* unwind_start will skip the first regs frame */
+ unwind_start(&state, current, regs, NULL);
+ pc = unwind_get_return_address(&state);
}
return pc;
}
--
2.17.1
Just ping... Or has profile code already been obsoleted?
On 2023/2/24 10:18, chenzhongjin wrote:
> Syzbot has been reporting the problem of stack-out-of-bounds in
> profile_pc for a long time:
> https://syzkaller.appspot.com/bug?extid=84fe685c02cd112a2ac3
>
> profile_pc tries to get pc if current regs is inside lock function. For
> !CONFIG_FRAME_POINTER it used a hack way to get the pc from stack, which
> is not work with ORC. It makes profile_pc returns wrong result, and
> frequently triggers KASAN.
>
> This can be fixed by using the unwind_start, it will skip the first
> regs frame and get the caller of lock function directly, or 0 if
> unwind_get_return_address finds the unwinding failed. For all of FP, ORC
> and guess unwinders it works.
>
> Fixes: 0cb91a229364 ("[PATCH] i386: Account spinlocks to the caller during profiling for !FP kernels")
> Reported-by: [email protected]
> Signed-off-by: Chen Zhongjin <[email protected]>
> ---
> arch/x86/kernel/time.c | 20 ++++++--------------
> 1 file changed, 6 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
> index e42faa792c07..5e0446f49906 100644
> --- a/arch/x86/kernel/time.c
> +++ b/arch/x86/kernel/time.c
> @@ -24,26 +24,18 @@
> #include <asm/timer.h>
> #include <asm/hpet.h>
> #include <asm/time.h>
> +#include <asm/unwind.h>
>
> unsigned long profile_pc(struct pt_regs *regs)
> {
> unsigned long pc = instruction_pointer(regs);
>
> if (!user_mode(regs) && in_lock_functions(pc)) {
> -#ifdef CONFIG_FRAME_POINTER
> - return *(unsigned long *)(regs->bp + sizeof(long));
> -#else
> - unsigned long *sp = (unsigned long *)regs->sp;
> - /*
> - * Return address is either directly at stack pointer
> - * or above a saved flags. Eflags has bits 22-31 zero,
> - * kernel addresses don't.
> - */
> - if (sp[0] >> 22)
> - return sp[0];
> - if (sp[1] >> 22)
> - return sp[1];
> -#endif
> + struct unwind_state state;
> +
> + /* unwind_start will skip the first regs frame */
> + unwind_start(&state, current, regs, NULL);
> + pc = unwind_get_return_address(&state);
> }
> return pc;
> }
On 4/2/2023 6:24 PM, Chen Zhongjin wrote:
> Just ping... Or has profile code already been obsoleted?
I think it would be reasonable to remove the locked functions hack since
lock profiling can be handled with much better other tools these days.
I wouldn't make it depend on the generic unwinder since such a low level
facility is likely better off without complex dependencies that could break.
-Andi
On 2023/4/4 2:29, Andi Kleen wrote:
>
> On 4/2/2023 6:24 PM, Chen Zhongjin wrote:
>> Just ping... Or has profile code already been obsoleted?
>
>
> I think it would be reasonable to remove the locked functions hack
> since lock profiling can be handled with much better other tools these
> days.
>
> I wouldn't make it depend on the generic unwinder since such a low
> level facility is likely better off without complex dependencies that
> could break.
>
> -Andi
>
>
Although now the generic unwinder on x86 is quite stable... I think it's
acceptable to remove the locked functions unwinding
for !FP case and leave the FP part as is.
I'll send a new patch for this with another bugfix.
Thanks for review and best,
Chen